com.google.javascript.jscomp

Class Es6ToEs3ClassSideInheritance

java.lang.Object

com.google.javascript.jscomp.Es6ToEs3ClassSideInheritance

All Implemented Interfaces:

CompilerPass, HotSwapCompilerPass

public final class Es6ToEs3ClassSideInheritance
extends java.lang.Object
implements HotSwapCompilerPass

Rewrites static inheritance to explicitly copy inherited properties from superclass to subclass so that the typechecker knows the subclass has those properties.

For example, the main transpilation passes will convert this ES6 code:

   class Foo { static f() {} }
   class Bar extends Foo {}
 

to this ES3 code:

   function Foo() {}
   Foo.f = function() {};
   function Bar() {}
   $jscomp.inherits(Bar, Foo);
 

and then this class will convert that to

   function Foo() {}
   Foo.f = function() {};
   function Bar() {}
   $jscomp.inherits(Bar, Foo);
   Bar.f = Foo.f;
 

Additionally, there are getter and setter fields which are transpiled from:

   class Foo { static get prop() { return 1; } }
   class Bar extends Foo {}
 

to:

   var Foo = function() {};
   Foo.prop; // stub declaration so that the type checker knows about prop
   Object.defineProperties(Foo, {prop:{get:function() { return 1; }}});

   var Bar = function() {};
   $jscomp.inherits(Bar, Foo);
 

The stub declaration of Foo.prop needs to be duplicated for Bar so that the type checker knows that Bar also has this property. (ES5 clases don't have class-side inheritance).

   var Bar = function() {};
   Bar.prop;
   $jscomp.inherits(Bar, Foo);
 

In order to gather the type checker declarations, this pass gathers all GETPROPs on a class. In order to determine which of these are the stub declarations it filters them based on names discovered in Object.defineProperties. Unfortunately, we cannot simply gather the defined properties because they don't have the type information (JSDoc). The type information is stored on the stub declarations so we must gather both to transpile correctly.

TODO(tdeegan): In the future the type information for getter/setter properties could be stored in the defineProperties functions. It would reduce the complexity of this pass significantly.

Constructor Summary

Constructors

Constructor and Description
Es6ToEs3ClassSideInheritance(AbstractCompiler compiler)

Method Summary

Modifier and Type	Method and Description
void	hotSwapScript(Node scriptRoot, Node originalRoot) Process the JS with root node root.
void	process(Node externs, Node root) Process the JS with root node root.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Es6ToEs3ClassSideInheritance

public Es6ToEs3ClassSideInheritance(AbstractCompiler compiler)

Method Detail

process

public void process(Node externs,
                    Node root)

Description copied from interface: CompilerPass

Process the JS with root node root. Can modify the contents of each Node tree

Specified by:

process in interface CompilerPass

Parameters:

externs - Top of external JS tree

root - Top of JS tree

hotSwapScript

public void hotSwapScript(Node scriptRoot,
                          Node originalRoot)

Description copied from interface: HotSwapCompilerPass

Process the JS with root node root. This is supposed to be significantly faster compared to corresponding full-compiler passes.

Specified by:

hotSwapScript in interface HotSwapCompilerPass

Parameters:

scriptRoot - Root node corresponding to the file that is modified, should be of type Token.SCRIPT.

originalRoot - Root node corresponding to the original version of the file that is modified. Should be of type token.SCRIPT.